The present invention relates to a recording medium such as a magnetic disk, a magneto optical disk or an optical disk, etc.
As materials for an optical disk substrate, polycarbonate or polymethyl methacrylate are proposed from the view points of forming or transparency.
By the way, such plastic materials have the following weak points.
(1) Insufficient in resistance to scuffing. PA1 (2) Easy to be charged by static electricity. PA1 (3) Easy to be adhered by dust and dirt. PA1 (a) a compound A having a (meth)acryloyl group; and PA1 (b) a reactive antistatic agent B having a quaternary ammonium salt group, an alkylene glycol chain, a hydrocarbon group of which carbon number is four or more, and a copolymerizable group. PA1 (a) 5 to 70% by weight (preferably 5 to 50% by weight) of a monomer represented by the following formula [O.sub.10 ] ##STR1## (where, R.sub.11 represents H or CH.sub.3. R.sub.12, R.sub.13, R.sub.14 represent H, alkyl group (especially alkyl group of which carbon number is in 1 to 9) or hydroxy-alkyl group (especially hydroxy-alkyl group of which carbon number is in 1 to 9). A represents alkylene group (especially alkylene group of which carbon number is in 1 to 10) or hydroxy-alkyl group (especially hydroxy-alkyl group of which carbon number is in 1 to 10). X.sup.31 represents an anion, for example, CH.sub.3 SO.sub.4.sup.31 , C.sub.2 H.sub.5 SO.sub.4.sup.31 , Cl.sup.31 , Br.sup.31 , H.sub.2 PO.sub.4.sup.31 , H.sub.2 PO.sub.4.sup.31 , CH.sub.3 COO.sup.31 , CH.sub.3 SO.sub.3.sup.31 , NO.sub.2.sup.31 , etc. (preferably, CH.sub.3 SO.sub.4.sup.31 , C.sub.2 H.sub.5 SO.sub.4.sup.31 , Cl.sup.31 , Br.sup.31)); PA1 (b) 10 to 80% by weight of a monomer represented by the following formula [O.sub.2 ] ##STR2## (where, R.sub.11 represents H or CH.sub.3. R.sub.15 represents alkylene group (especially alkylene group of which carbon number is in 2 to 4). R.sub.16 represents H, alkyl group (especially alkyl group of which carbon number is in 1 to 10) or aryl group (especially aryl group of which carbon number is in 6 to 10). m is an integer in a range of 1 to 25.); and PA1 (c) 10 to 70% by weight (desirably 10 to 40% by weight) of a monomer represented by the following formula [O.sub.3 ] ##STR3## where, R.sub.11 represents H or CH.sub.3. R.sub.12 represents H or (meth)acryloyl group. n is an integer in a range of 4 to 30.) PA1 (a') 5 to 70% by weight (desirably 5 to 50% by weight) of an amine monomer represented by the following formula [O.sub.11 ] ##STR4## (where, R.sub.11 represents H or CH.sub.3. R.sub.12, R.sub.13 represent H, alkyl (especially alkyl group of which carbon number is in 1 to 9) group or hydroxy-alkyl group (especially hydroxy-alkyl group of which carbon number is in 1 to 9). A represents alkylene group (especially alkylene group of which carbon number is in 1 to 10) or hydroxy-alkyl group (especially hydroxy-alkyl group of which carbon number is in 1 to 10).); PA1 (b) 10 to 80% by weight of a monomer represented by the above-mentioned formula [O.sub.2 ]. PA1 (c) 10 to 70% by weight (desirably 10 to 40% by weight) of a monomer represented by the above-mentioned formula [O.sub.3 ]. PA1 (a) a compound A.sub.1 selected from a group of (meth)acrylate having three or more (meth)acryloyl groups; and PA1 (b) a compound A.sub.2 selected from a group of (meth)acrylate having two (meth)acryloyl groups and an ethylene glycol chain; PA1 (1) High hardness by crosslink structure of the compound A. PA1 (2) Long chain component of hydrocarbon of the reactive antistatic agent B promotes concentration of the reactive antistatic agent B itself on the surface layer in the curing step. By the reason, even a small amount of the reactive antistatic agent B show good antistatic characteristics. Also its transparency is excellent. PA1 (3) The compound B has quaternary ammonium salt group and ethylene glycol chain. Therefore, it has good antistatic characteristics even under low humidity. PA1 (4) The compound A and the reactive antistatic agent B are fixed on the surface of a base. Therefore, its antistatic ability is not lost if the surface is wiped up with a cloth and the like. PA1 (5) When the oligomer O is used, the amount of the reactive antistatic agent B can be reduced. When the amount of the reactive antistatic agent B is reduced, its hardness becomes better. Additionally, film adherence is improved. PA1 (6) When the silicone C is used, the surface energy is low. Therefore, its resistance to contamination is good. More, lubricating properties are also improved, so that the surface is kept against scratches
For the above reasons, it is proposed to provide a film that is transparent, rich in resistance to scuffing and has electrostatic protection ability on the surface of recording medium.
A method, for example, is known to provide a hard coating film added by a conductive filler on the surface. Also, a method to provide a hard coating film mixed by a surface active agent is known.
For the former, however, a large amount of conductive filler must be added to meet electrostatic protection characteristics. As the result, its optical characteristics (transparency) or hardness is deteriorated. Additionally, it becomes difficult to perform coating work.
For the latter, it is difficult to expect sufficient effect under low humidity. Also, it has some other problems such as cloudiness or loss of electrostatic protection ability because of occurrence of bleeding phenomenon.
For dealing with such problems, for example, an coating material (a mixture of thiocyanate, an anionic surface active agent having an alkylene glycol chain, a copolymerizable (meth)acrylate and optical polymerization initiator) is proposed (Japanese Patent Laid-Open No.4-80266(1992)). In addition to this, electrostatic preventive compositions are proposed in Japanese Patent Laid-Open No.4-33968(1992) and Japanese Patent Laid-Open No.3-275705 (1991).
A composition by the above proposals, however, has not sufficient electrostatic preventive ability.
Additionally, contamination is not caused only by adherence of dust or dirt by static electricity. There is, however, contamination by oil adhesive materials or water soluble adhesive materials.
For avoiding such contamination and for easily removing it, it is necessary to reduce surface energy of the coating materials.
By the way, surface energy of the above-mentioned materials for treating the surface is high, so that contamination by adherence of oil adhesive materials or water soluble adhesive materials can not be ignored.